This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 2000-222892 filed on Jul. 24, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a brake control device for a vehicle. More particularly, the present invention pertains to a vehicle brake control device having a hydraulic pressure generating device operable in response to operation of a brake pedal and operable independently of operation of the brake pedal. The present invention is applicable specifically for use in steering control by braking (vehicle slide slip preventing control) and traction control.
A known brake control device for a vehicle is disclosed in published European Patent Application No. 0 379 329 A2 which corresponds to a Japanese Patent Application published as Toku-Kai-Hei 2(1990)-241863). This known brake control device includes a master cylinder for generating a hydraulic pressure to be supplied to wheel brake cylinders associated with road wheels of the vehicle, a booster for activating the master cylinder in response to operation of a brake pedal, an electro-magnetic valve device for activating the booster independently of the operation of the brake pedal, and a plurality of modulators interposed between the master cylinder and each of the wheel cylinders for regulating the hydraulic pressure to the corresponding wheel brake cylinder supplied from the master cylinder. When the driving road wheel is spinning, the booster is automatically activated by the electro-magnetic valve device to activate the master cylinder. Braking torque is applied to a controlled road wheel which is spinning, independently of a brake pedal operation, so that traction control is executed. While the traction control is being executed, the non-controlled road wheel, which is not driven, is disconnected from the master cylinder.
According to this known brake control device, the non-controlled road wheel is always disconnected from the master cylinder while the traction control is being executed. When the brake pedal is depressed by a driver when the traction control is being executed, a vehicle deceleration corresponding to the brake pedal depression is not able to be generated. Further, when this known brake control device is applied for use in other automatic brake control devices including steering control by braking, the same drawback occur.
Thus, this known vehicle brake control device is susceptible of certain improvements with respect to generating vehicle deceleration corresponding to the brake pedal depression when the brake pedal is depressed while the automatic brake control is being applied to the controlled road wheel.
Accordingly, a need exists for an improved brake control device which generates vehicle deceleration corresponding to brake pedal depression when the brake pedal is depressed while the automatic brake control is being performed. A need also exists for a an improved brake control device that is able to achieve sufficient brake pedal operation when the brake operation is performed by the driver.
According to an aspect of the present invention, a brake control device for a vehicle includes a brake pedal, a brake pedal operational condition detecting device for detecting an operational condition of the brake pedal, first and second wheel brake cylinders responsive to supplied hydraulic pressure for applying brake torque to the first and second road wheels, respectively, and a hydraulic pressure generating device for generating hydraulic pressure in response to operation of the brake pedal and for generating hydraulic pressure independently of the operation of the brake pedal. The hydraulic pressure generating device is hydraulically connected to the first and second wheel cylinders. A hydraulic pressure control valve device is disposed between the hydraulic pressure generating device and the first wheel brake cylinder for regulating hydraulic pressure in the first wheel cylinder supplied from the hydraulic pressure generating device, and is disposed between the hydraulic pressure generating device and the second wheel brake cylinder for regulating hydraulic pressure in the second wheel brake cylinder supplied from the hydraulic pressure generating device independently of regulation for hydraulic pressure in the first wheel brake cylinder. A first control device responsive to vehicle motion under the non-operated condition of the brake pedal is provided for activating the hydraulic pressure generating device, and for activating the hydraulic pressure control valve device to supply hydraulic pressure to one of the first and second wheel brake cylinders corresponding to one of the first and second road wheels to be controlled in response to the vehicle motion and to regulate hydraulic pressure in the one wheel brake cylinder, and to inhibit supplying hydraulic pressure to the other of the first and second wheel brake cylinders corresponding to the other of the first and second road wheels to be not controlled in response to the vehicle motion. In addition, a second control device responsive to the brake pedal operational condition detected by the brake pedal operational condition detecting device under the activated condition of the hydraulic pressure control valve device by the first control means controls the operation of the hydraulic pressure control valve device to supply hydraulic pressure to the other wheel brake cylinder without obstructing hydraulic pressure regulating performance of the first control means with respect to the one wheel brake cylinder.
Therefore, when the brake pedal is operated under the automatic brake control by the first control means, a proper response to the brake pedal operation is generated.
The brake control device for the vehicle further includes a vehicle deceleration detecting device for detecting or estimating vehicle deceleration. The second control device includes a target vehicle deceleration calculating mechanism for calculating the target vehicle deceleration on the basis of the brake pedal operational condition detected by the brake pedal operational condition detecting device, a vehicle deceleration comparing mechanism for comparing the target vehicle deceleration calculated by the target vehicle deceleration calculating mechanism with the vehicle deceleration detected or estimated by the vehicle deceleration detecting mechanism, and a valve control device responsive to an output by the vehicle deceleration comparing mechanism for controlling the pressure control valve device so that the vehicle deceleration resembles the target vehicle deceleration by regulating the brake pressure in the other wheel brake cylinders. The brake pedal operational condition detecting device includes a stroke sensor for detecting the operational stroke of the brake pedal. The valve control device controls the operation of the hydraulic pressure control valve device so as to increase hydraulic pressure in the other wheel brake cylinder when the vehicle deceleration becomes equal to the target vehicle deceleration.
Therefore, when the automatic brake control is performed when the brake pedal is being operated, vehicle deceleration corresponding to the brake pedal operation is generated. The wheel brake cylinders associated with all the road wheels are prevented from being cut off from the master cylinder and a sufficient brake pedal operation is thus achieved when the brake operation is performed by the driver.
It is preferable that the first control device performs a steering control by braking or a traction control. The steering control by braking is performed for activating the hydraulic pressure control valve device to supply the brake pressure to the one wheel cylinder in accordance with the vehicle motion under the oversteer restraining control or understeer restraining control when the brake pedal is under the non-controlled operation and for applying braking force to a vehicle portion at which the one road wheel is mounted on the vehicle. The traction control is performed for activating the hydraulic pressure control valve device to apply the brake torque to the driving road wheel in response to an acceleration slip ratio of the driving road wheel under the brake pedal being non-operated while the vehicle is being accelerated.
The hydraulic pressure control valve device preferably includes a first hydraulic pressure control valve disposed between the hydraulic pressure generating device and the first wheel brake cylinder, and a second hydraulic pressure control valve operable independently of operation of the first pressure control valve disposed between the hydraulic pressure generating device and the second wheel brake cylinder.
In addition, the hydraulic pressure generating device preferably includes a reservoir containing brake fluid, a master cylinder for generating a hydraulic pressure by increasing pressure of the brake fluid, a fluid pressure booster for activating the master cylinder in response to the operation of the brake pedal, a booster driving device for activating the fluid pressure booster independently of the operation of the brake pedal, and a brake pedal remaining mechanism for maintaining the brake pedal at an initial position thereof while the fluid pressure booster is being activated by the booster driving device.
The fluid pressure booster is preferably a vacuum booster having a movable wall operatively connected to the master cylinder, a constant pressure chamber defined at a front side of the movable wall and communicated with a vacuum source, a variable pressure chamber defined at a rear side of the movable wall, and a valve mechanism carried by the movable wall and operatively connected to the brake pedal for controlling communication between the constant pressure chamber and the variable pressure chamber and communication between the variable pressure chamber and the atmosphere in response to the brake pedal operation. The booster driving device includes a solenoid carried by the movable wall and operatively connected to the valve mechanism. The brake pedal remaining mechanism includes a first input member operatively connected to the brake pedal and movable in accordance with the brake pedal operation, and a second input member operatively connect to the valve mechanism, with the second member being movable forward with the first input member as a unit to operate the valve mechanism when the brake pedal is operated and being movable forward with the movable wall of the vacuum booster relative to the first input member when the vacuum booster is activated by the booster driving device under the non-operated condition of the brake pedal.
According to another aspect of the invention, a brake control device for a vehicle having first and second road wheels includes a brake pedal, a brake pedal sensor operatively connected to the brake pedal for detecting an operational condition of the brake pedal, a first wheel brake cylinder receiving hydraulic pressure to apply brake torque to the first road wheel, a second wheel brake cylinder receiving hydraulic pressure to apply brake torque to the second road wheel, and a hydraulic pressure generating device which generates both hydraulic pressure in response to operation of the brake pedal and hydraulic pressure independently of operation of the brake pedal, with the hydraulic pressure generating device being hydraulically connected to the first and second wheel cylinders. A first hydraulic pressure control valve is disposed between the hydraulic pressure generating device and the first wheel brake cylinder for regulating hydraulic pressure in the first wheel cylinder supplied from the hydraulic pressure generating device, and a second hydraulic pressure control valve is disposed between the hydraulic pressure generating device and the second wheel brake cylinder for regulating hydraulic pressure in the second wheel brake cylinder supplied from the hydraulic pressure generating device independently of regulation of hydraulic pressure in the first wheel brake cylinder. A first control device is responsive to vehicle motion under a non-operated condition of the brake pedal for activating the hydraulic pressure generating device and activating the first hydraulic pressure control valve device to supply hydraulic pressure to the first wheel brake cylinder of the first road wheel to be controlled in response to the vehicle motion and to regulate hydraulic pressure in the first wheel brake cylinder, while also inhibiting supply of hydraulic pressure to the second wheel brake cylinder corresponding to the second road wheel which is not to be controlled in response to vehicle motion. A vehicle deceleration detecting mechanism detects or estimates vehicle deceleration, a target vehicle deceleration calculating mechanism calculates a target vehicle deceleration based on the brake pedal operational condition detected by the brake pedal sensor, and a vehicle deceleration comparing mechanism compares the target vehicle deceleration calculated by the target vehicle deceleration calculating mechanism with the detected or estimated vehicle deceleration provided by the vehicle deceleration detecting mechanism. A valve control is responsive to an output by the vehicle deceleration comparing mechanism for controlling operation of the second hydraulic pressure control valve device to cause the detected or estimated vehicle deceleration to equal the target vehicle deceleration by regulating hydraulic pressure in the second wheel brake cylinder without obstructing hydraulic pressure regulating performance of the first control device with respect to the first wheel brake cylinder.